An Optimized O9-1/Hydrogel System for Studying Mechanical Signals in Neural Crest Cells

Summary

Detailed step-by-step protocols are described here for studying mechanical signals in vitro using multipotent O9-1 neural crest cells and polyacrylamide hydrogels of varying stiffness.

Abstract

Neural crest cells (NCCs) are vertebrate embryonic multipotent cells that can migrate and differentiate into a wide array of cell types that give rise to various organs and tissues. Tissue stiffness produces mechanical force, a physical cue that plays a critical role in NCC differentiation; however, the mechanism remains unclear. The method described here provides detailed information for the optimized generation of polyacrylamide hydrogels of varying stiffness, the accurate measurement of such stiffness, and the evaluation of the impact of mechanical signals in O9-1 cells, a NCC line that mimics in vivo NCCs.

Hydrogel stiffness was measured using atomic force microscopy (AFM) and indicated different stiffness levels accordingly. O9-1 NCCs cultured on hydrogels of varying stiffness showed different cell morphology and gene expression of stress fibers, which indicated varying biological effects caused by mechanical signal changes. Moreover, this established that varying the hydrogel stiffness resulted in an efficient in vitro system to manipulate mechanical signaling by altering gel stiffness and analyzing the molecular and genetic regulation in NCCs. O9-1 NCCs can differentiate into a wide range of cell types under the influence of the corresponding differentiation media, and it is convenient to manipulate chemical signals in vitro. Therefore, this in vitro system is a powerful tool to study the role of mechanical signaling in NCCs and its interaction with chemical signals, which will help researchers better understand the molecular and genetic mechanisms of neural crest development and diseases.

Introduction

Neural crest cells (NCCs) are a group of stem cells during vertebrate embryogenesis with a remarkable ability to migrate and contribute to the development of various organs and tissues. NCCs can differentiate into different cell types, including sensory neurons, cartilage, bone, melanocytes, and smooth muscle cells, depending on the location of axial origin and the local environmental guidance of the NCC^1,2. With the ability to differentiate into a wide array of cell types, genetic abnormalities that cause dysregulation at any stage of neural crest (NC) development can lead to numerous congenital diseases

Protocol

1. Hydrogel preparation

NOTE: All steps must be performed in a cell culture hood that has been disinfected with ethanol and ultraviolet (UV)-sterilized before use to maintain sterility. Tools, such as tweezers and pipettes, must be sprayed with ethanol. Buffer solutions must also be sterile-filtered.

1. Preparation of aminosilane-coated glass coverslips
   1. Place the desired number of glass coverslips onto a piece of laboratory wipe.
      NOTE: Prepare an additional 3-4 coverslips to ensure sufficient backup supplies as they break easily. Different materials of glass coverslips will yield different compatibility of cell ....

Results

Hydrogel preparation and stiffness assessment through AFM and the Hertz model
Here, a detailed protocol is provided to generate polyacrylamide hydrogels of varying stiffness by regulating the ratio of acrylamide and bis-acrylamide. However, the polyacrylamide hydrogels are not ready for the adhesion of cells due to the lack of ECM proteins. Thus, sulfo-SANPAH, acting as a linker, covalently binds to the hydrogels and reacts with the primary amines of ECM proteins to allow the adhesion of ECM protei.......

Discussion

The goal of the current study is to provide an effective and efficient in vitro system to better understand the impact of mechanical signals in NCCs. In addition to following the step-by-step protocol mentioned above, researchers need to keep in mind that the cell culture of O9-1 NCCs is affected by the type of glass coverslips used to prepare hydrogels. For instance, it was noted that cells seeded on a specific type of glass coverslip (see the Table of Materials) survived and proliferated .......

Materials

Name	Company	Catalog Number	Comments
12 mm #1 Corning 0211 Glass Coverslip	Chemglass Life Sciences	CLS-1763-012
2% Bis-Acrylamide	Sigma Aldrich	M1533
24-well plate	Greiner Bio-one	662165
25 mm #1 Corning 0211 Glass Coverslip	Chemglass Life Sciences	CLS-1763-025
3-aminopropyl triethoxysilane (APTS)	Sigma Aldrich	A3648
4-well cell culture plate	Thermo Scientific	179830
4% Paraformaldehyde	Sigma Aldrich	J61899-AP
40% Acrylamide	Sigma Aldrich	A4058
50% glutaraldehyde	Sigma Aldrich	G7651
6-well cell culture plate	Greiner Bio-one	657160
AFM cantilever (spherical bead)	Novascan
AFM software	Catalyst NanoScope		Model: 8.15 SR3R1
Alexa Fluor 488 Phalloidin	Thermo Fisher	A12379
Ammonium Persulfate (APS)	Sigma Aldrich	248614	Powder
anti-AP-2α Antibody	Santa Cruz	sc-12726
anti-Vinculin antibody	Abcam	ab129002
Atomic Force Microscopy (AFM) Bioscope Catalyst	Bruker Corporation
Collagen type I (100mg)	Corning	354236
DAPI (4',6-Diamidino-2-Phenylindole, Dihydrochloride)	Thermo Fisher	D1306
Dichloromethylsilane (DCMS)	Sigma Aldrich	440272
Donkey serum	Sigma Aldrich	D9663
Dulbecco's Modified Eagle Medium (DMEM)	Corning	10-017-CV
Fetal bovine serum (FBS)	Corning	35-010-CV
Fluorescence microscope	Leica		Model DMi8
Fluoromount-G mounting medium	SouthernBiotech	0100-35
HEPES	Sigma Aldrich	H3375	Powder
Horse serum	Corning	35-030-CI
iScript Reverse Transcription Supermix	Bio-Rad	1708841
Penicillin-Streptomycin antibiotic	Thermo Fisher	15140148
RNeasy micro kit	Qiagen	74004
Sterile 1x PBS	Hyclone	SH30256.02
Sterile deionized water	Hardy Diagnostics	U284
sulfo-SANPAH	Thermo Fisher	22589
SYBR green	Applied Biosystems	4472908
TEMED	Sigma Aldrich	T9281
Triton X-100	Sigma Aldrich	X100
Tween 20	Sigma Aldrich	P9416